Why did the Soviet Union place nuclear missiles on Cuba

The USSR must have known that it would cause a crisis. They had no attempt at all to camouflage the sites, and even allowed the missiles to travel on open deck. This has caused much debate as to what Khrushchev was really doing. Some explanations include, to bargain with USA, to test the USA, to trap the USA, to close the missile gap, to defend cuba, to strengthen his own position in the USA